Atm. Profile (07_L2)

Product Description:

The MODIS Atmospheric Profile product consists of several parameters: they are total-ozone burden, atmospheric stability, temperature and moisture profiles, and atmospheric water vapor. All of these parameters are produced day and night for Level 2 at 5x5 1-km pixel resolution when at least 9 FOVs are cloud free. There are two MODIS Atmosphere Profile data product files: MOD07_L2, containing data collected from the Terra platform; and MYD07_L2, containing data collected from the Aqua platform.

The MODIS total-ozone burden is an estimate of the total-column tropospheric and stratospheric ozone content. The MODIS atmospheric stability consists of three daily Level 2 atmospheric stability indices. The Total Totals (TT), the Lifted Index (LI), and the K index (K) are each computed using the infrared temperature- and moisture-profile data, also derived as part of MOD07. The MODIS temperature and moisture profiles are produced at 20 vertical levels. A clear sky synthetic regression retrieval algorithm is used, where regression coefficients are derived by using a fast radiative transfer model with atmospheric characteristics taken from a dataset of global (radiosonde and model) profiles. The MODIS atmospheric water-vapor product is an estimate of the total column water vapor made from integrated MODIS infrared retrievals of atmospheric moisture profiles in clear scenes. “Water_Vapor Low” and “Water_Vapor_High” are also produced to give information about the vertical distribution of moisture within three (low, middle and high) layers of the troposphere.

Research and Application

Total-column ozone estimates at MODIS resolution are required by MODIS investigators developing atmospheric correction algorithms. This information is crucial for accurate land and ocean-surface-parameter retrievals. Furthermore, strong correlations have been found to exist between the meridional gradient of total ozone and the wind velocity at tropopause levels, providing the potential to predict the position and intensity of jet streams. Total-column ozone monitoring is also important due to the potential harm to the environment caused by anthropogenic depletion of ozone.

Atmospheric instability measurements are predictors of convective-cloud formation and precipitation. The MODIS instrument offers an opportunity to characterize gradients of atmospheric stability at high resolution and greater coverage. Radiosonde-derived stability indices are limited by the coarse spacing of the point-source data, too large to pinpoint local regions of probable convection.

Atmospheric temperature and moisture sounding data at high spatial resolution from MODIS and high spectral resolution sounding data from AIRS provides a wealth of new information on atmospheric structure in clear skies. The profiles are used to correct for atmospheric effects for some of the MODIS products (e.g., sea-surface and land-surface temperatures, ocean aerosol properties, water-leaving radiances, and PAR) as well as to characterize the atmosphere for global greenhouse studies.

Total-column precipitable-water estimates at MODIS resolution are required by MODIS investigators developing atmospheric-correction algorithms. This information is crucial for accurate land and ocean surface-parameter retrievals. MODIS also provides finer horizontal-scale atmospheric water vapor gradient estimates than are currently available from the POES satellites.

Data Set Evolution

Temperature, moisture and ozone profile retrieval algorithms are adapted from the International TOVS Processing Package (ITPP), taking into account the lack of stratospheric channels and far higher horizontal resolution of MODIS. The profile retrieval algorithm requires calibrated, navigated, and coregistered 1-km FOV radiances from MODIS channels 25, 27-29, and 30-36. The MODIS cloud mask (MOD35_L2) is used for cloud screening. The algorithm also requires NCEP analysis of surface pressure.

Atmospheric-stability estimates are derived from the MODIS temperature and moisture retrievals contained in this product. Layer temperature and moisture values may be used to estimate the temperature lapse rate of the lower troposphere and the low-level moisture concentration.

Several algorithms for determining atmospheric water vapor, or precipitable water, exist. It is most directly achieved by integrating the moisture profile through the atmospheric column. Other, split-window, methods also exist. This class of techniques uses the difference in water-vapor absorption that exists between channel 31 (11 µm) and channel 32 (12 µm).

Data validation is conducted by comparing results to in situ radiosonde, Microwave Radiometer and GPS measurements, Brewer spectrophotometer measurements. In addition, retrievals from other satellites are also used for validation, including the GOES sounder moisture and ozone products, AIRS profiles, the Special Sensor Microwave/Imager (SSM/I), Total Ozone Mapping Spectrometer (TOMS) and Ozone Monitoring Instrument (OMI). Quality control consists of manual and automatic inspections, with regional and global mean temperatures at 300, 500, and 700 hPa, along with atmospheric water vapor and Total Ozone.